1. Field of the Invention
The present invention relates to an organic light emitting device (OLED) in which a phenanthroline-fused phenazine or its derivative is used as an emissive layer, an electron transport layer, a hole-blocking layer, and/or a host material.
2. Description of the Related Art
OLEDs are commercially attractive for various display applications due to their high efficiency, low driving voltage, wide color range, light weight, simple device fabrication and potential low cost. Great efforts have been made to develop effective materials for use in these devices.
OLEDs typically comprise an emissive layer sandwiched between a transparent anode, such as transparent indium tin oxide (ITO), and a metal cathode, such as Mg, Al, Ag or their alloys. When a bias is applied across the electrodes, holes and electrons are respectively injected from the anode and cathode into the emissive layer, typically facilitated by hole transport and electron transport layers adjacent to the respective electrodes. The holes and electrons radiatively combine in the emissive layer and emit light.
In many cases, the doping of a functional material into a host material may lead to improved performance. Improved performance also may be achieved through the utilization of blocking layers, which block either holes or electrons from escaping the device.
Because of consumer expectations of good efficiency, long lifetime and pure color for OLEDs, a need exists for the development of effective materials for use in these devices.
It is an object of the invention to provide an improved OLED in which phenanthroline-fused phenazine or its derivative is used as an emissive layer, an electron transport layer, a hole-blocking layer, and/or a host material for a functional dopant.
Thus, in one aspect, the invention is an OLED in which an organic layer is sandwiched between an anode and a cathode, and in which the organic layer includes a phenanthroline-fused phenazine based compound.
In one embodiment of the invention, the phenanthroline-fused phenazine based compound is 1,10-phenanthroline-fused phenazine with the following structure: 
wherein R1 to R8 independently represent H, an alkyl group, an alkoxy group, or an aromatic group.
In another embodiment of the invention, the phenanthroline-fused phenazine based compound is 1,7-phenanthroline-fused phenazine with the following structure: 
wherein R1 to R8 independently represent H, an alkyl group, an alkoxy group, or an aromatic group.
In another embodiment of the invention, the phenanthroline-fused phenazine based compound is a 4,7-phenanthroline-fused phenazine with the following structure: 
wherein R1 to R8 independently represent H, an alkyl group, an alkoxy group, or an aromatic group.
In another embodiment of the invention, the phenanthroline-fused phenazine based compound is 1,10-phenanthroline-fused phenazine of the following structure: 
wherein R1 to R8 independently represent H, an alkyl group, an alkoxy group, or an aromatic group; X represents O, S, NR, with R being H or an alkyl group, CH2, CH2CH2, or a fused or substituted aromatic group; and n is an integer from 1 to 12, wherein X may not be present when n is 1.
In another embodiment of the invention, the phenanthroline-fused phenazine based compound is 1,7 phenanthroline of the following structure: 
wherein R1 to R8 independently represent H, an alkyl group, an alkoxy group, or an aromatic group; X represents O, S, NR, with R being H or an alkyl group, CH2, CH2CH2, or a fused or substituted aromatic group; and n is an integer from 1 to 12, wherein X may not be present when n is 1.
In another embodiment of the invention, the phenanthroline-fused phenazine is 4,7-phenanthroline-fused phenazine with the following structure: 
wherein R1 to R8 independently represent H, an alkyl group, an alkoxy group, or an aromatic group; X represents O, S, NR, with R being H or an alkyl group, CH2, CH2CH2, or a fused or substituted aromatic group; and n is an integer from 1 to 12, wherein X may not be present when n is 1.
Some preferred phenanthroline-fused phenazine based compounds are listed below: 
wherein R9 and R10 independently are H, CH3 or another alkyl group; 
wherein X is O, S, NR, with R being H, CH3 or another alkyl group, CH2 or CH2CH2.
1,7 phenanthroline-fused phenazine or 4,7 phenanthroline-fused phenazine may be substituted for 1,10 phenanthroline-fused phenazine in the above-listed structures.
According to the invention, the phenanthroline-fused phenazine based compound can be used as an emissive layer, a hole blocking layer, and/or an electron transport layer. Further, the compound can be used as a host material for a functional guest material. The functional guest material may be an emitter, a hole-blocker, and/or an electron transporter.
The phenanthroline-fused phenazine based compound can be used in both electro-fluorescent and electro-phosphorescent OLEDs.